The present invention relates to an evacuated heat insulation unit (hereinafter referred to as evacuated insulation unit) for use in, for example, refrigerators as a heat insulation panel and a method of manufacturing the evacuated insulation unit.
The evacuated insulation unit for use in refrigerators has a synthetic resin bag containing a heat insulation material, such as a fine perlite powder, in a vacuum state. The evacuated insulation unit has a high heat insulating property or a low thermal conductivity of 0.01 Kcal/m.h. or less since it includes a heat insulation vacuum layer. However, over time, the heat insulating property of the evacuated insulation unit is degraded since a trace amount of air permeates through the plastic bag into the evacuated insulation unit. When the evacuated insulation unit is surrounded and covered with a foamed plastic resin, such as a foamed urethane resin, for securing it to a wall of a refrigerator as a heat insulation member by foaming the resin, air is prevented from entering into the plastic bag. However, Freon gas and carbon dioxide gas which are used for foaming the urethane resin, and which stay in the wall of the refrigerator, permeate through the plastic bag into the evacuated insulation unit. This lowers the degree of vacuum within the evacuated insulation unit. Thus, the heat insulation property of the insulation unit is deteriorated.
In order to avoid to this drawback, it has been proposed to charge an activated carbon into the plastic bag of the evacuated insulation unit together with the perlite powder for adsorbing Freon gas. However, no practical attempt has been made to prevent the evacuated insulation unit from being degraded in the degree of vacuum due to the carbon dioxide gas, as time passes. This results in a poor heat insulation property for the unit.